جستجوی مقالات مرتبط با کلیدواژه "stope" در نشریات گروه "مهندسی معدن"

The over-break and slough of walls and roof of stopes in underground mines leads to unplanned dilution and dropping in the grade. The complex mechanism of unplanned dilution resulting from the effect of different parameters and interaction between them makes it impossible to provide an unplanned dilution model with sufficient accuracy through non-system methods. In this paper, a high-precision model in which interactions between parameters are considered is presented using the rock engineering systems approach. For this purpose, after selecting 8 parameters, as the most important parameters for unplanned dilution, the steps of this method include the formation of interaction matrix, matrix coding and formation of the ranking table, the index of unplanned dilution of 24 stopes from the Venarch Manganese mines has been calculated. Subsequently, using the cavity monitoring system, the actual values of unplanned dilution of each stope were measured and from there the unplanned dilution prediction model was obtained based on the unplanned dilution index. The model, which is a power relationship, has a coefficient of 0.89, root mean square error of 0.034, mean absolute error of 0.089 and a percentage of variance of 87. In the end, using this model, unplanned dilution of 9 new stopes (other than the 24 workshops) was predicted and compared with the actual values measured. The coefficient of this prediction is equal to 0.95, which indicates the high efficiency of the model and system approach in predicting the unplanned dilution of underground mining stopes.

The aim of stope limit optimization is to define an area with maximum economic value, for which, in accordance to the mining method used, all technical and geometrical constraints is considered. Although more than four decades have passed since the first presentation of underground stope optimizatiom algorithm, the development of these algorithms in comparison with similar algorithms used in open pit mines, have been very slow. This may be due to the high variety of underground mining methods and complexity of economic modeling of mining limit. In this paper a 3D comprehensive algorithm, which is called MLOA, is proposed. This algorithm runs on a variable value block models and is able to determine the number, height and optimal layout of levels. To determine the optimum limit of stopes, MLOA has used a heuristic algorithm which is called SOA. In SOA algorithm, Technical and geometrical constraints such as the minimum and maximum of stope dimension and minimum width of rib pillars have been regarded. The optimum location and dimension of stopes within specific level can be determined by using SOA. In order to verify the methods , the results of the application of SOA algorithm on hypothetical economic block model, are compared to similar rigorous algorithm’s results. The results demonstrate the capability of SOA algorithm in determining optimum limit of stopes.

Fetr6 is one of the Iran’s underground mines in which chromite had been extracted with room and pillar mining method. In Phase 1 of this mine، after the occurrence of a large scale failure، mining operations ceased and the stope and rib pillars mining method with delayed backfill was designed for phase 2. To design pillars in this method، it was necessary to understand the values of applied stress on pillars. Therefore، widespread and thorough studies were carried out to obtain them for this research. The values of applied stresses on pillars were estimated by numerical and empirical methods. Also، the effects of depth and sequence of ore extraction were investigated using both methods more precisely. The results show that while the plastic zone is not created in pillars، the estimated values by empirical methods are maximum 35% more than the real values and pillar position in the layout of mine is an important parameter on its stress values. But there are not meaningful differences between two methods when plastic zone is created in pillars.

Optimal pillar design has an important influence on optimization of mining operations in the stope and pillar mining method. Since the existing empirical methods developed for pillar design have some limitations، the application of numerical methods is widely increasing. Applying these methods، it is possible to consider some factors as the sequence of ore extraction in stopes and the impact of confined stresses imposed on pillars. In this research، using FLAC3D Software that includes the Mohr-Coulomb Strain Softening (MCSS) failure criterion، the distribution of vertical and horizontal stresses activated on pillars were evaluated considering sequences of extraction in stopes. At the end، the obtained results were implemented on pillars in the stope and pillar part (Phase No. 1) of Faryab chromite mine. The obtained results show that the optimal pillar size in the Phase No. 1 of Faryab mine is eight meters. With the real condition of Faryab mine، pillars width less than about 8 meters have been collapsed or are instable and other pillars are stable so far. These conditions are consistent with the results of this study. Moreover، in order to validate this numerical method، Tributary area theory and Lunder and Pakalnis equation have been considered. The comparison in horizontal stress distribution case showed that there is no relation between vertical and horizontal stress in pillar with the ratio of width to height less than 2/3. But in cases that pillars are stable and the ratio of width to height is more than 2/3، the horizontal stress distribution showed a parabolic curve that the maximum stress is at the middle of pillar. In this kind of pillars the numerical modeling results for horizontal stress is the same as Lunder and Pakalnis equation results.

Optimization of stope boundaries has received less attention than that in open pit mines. However، few algorithms are available for optimization of stope boundaries، which are either tailored for a specific mining method or lack some significant geometrical and technical constraints. A greedy algorithm is described in this paper for optimization of stope boundaries in each level of an underground mine. The algorithm employs a graph of the 2D economic block model in which weight of edges indicate cumulative economic values of blocks. The proposed algorithm enjoys Dijikstra approach to find the maximum path length on the graph. Dijikstra method is one of the best methods for solving the greedy algorithms. Indeed، the path which is searched in model of mining area using this algorithm، defines limits of the optimized stopes which provide the highest economic value.